Referring to FIGS. 1A and 1B, a conventional color wheel module 2 for use in a projection apparatus includes a spindle, a color wheel 4 mounted on the spindle, a motor 6 for driving the spindle and thus the color wheel 4, and a carrier bracket 8 for holding the motor 6. The color wheel 4 has a plurality of color regions 402. The color wheel 4 generally has 6 numbers of equidistant color regions 402, such as Red, Green and Blue. Since a light valve (not shown) is required to complement with the color regions 402 in the color wheel 4 in order to transform light beams into image beams, the rotation speed of the color wheel 4 is controlled in conformance with the switching speed of the light valve.
In order to ensure the rotation speed of the color wheel 4, a timing mark 10 is usually disposed on a lateral side 602 of the motor casing such that the timing mark 10 is aligned with an adjoining area between adjacent two color regions 402,404. A light source 12 and a detection device 14 are mounted on the carrier bracket 8. The timing mark 10 is generally black.
The light source 12 emits the light beams, Infra-red ray (IR) for example, ceaselessly onto the lateral side 602 of the motor casing which is kept under constant rotation. Because, the lateral side 602 is coated with silver to reflect the light beams, the detection device 14 is capable of detecting the reflected light beams. During rotation of the color wheel 4, the detection device 14 is unable to detect the reflected light beams once the light beams projecting on the timing mark 10, since black has poor reflection ability even cannot reflect the light beam. Under this condition, the position of the respective color region 402 in the color wheel 4 is located, thereby controlling the rotation speed of the color wheel 4.
It is noted that mounting of the timing mark 10 on the lateral side 602 of the motor casing is done manually. It is time wasting and lacks accuracy in the position. In the prior art, some control software is used to adjust the position of the timing mark 10 on the motor casing with respect to the light valve. However, employment of the software results in extra expense as well as time waste.